You would start by finding out how much 10 and 20 cost per copy
10: 40-25 = 15/10 = $1.50 dollars per copy
20 (This is for checking your math, not required): 55-25 = 30/20 = $1.50 dollars per copy
So, to find 15 copies you would use this formula: 25 + 1.5x
25 + 1.5(15)
25 + 22.5
$47.50 for 15 copies
Now for the second question:
160 - 25 = 135/1.5 = 90 copies
90 copies for $160
